How could the church belong to Jesus (Matthew 16:18) and yet be the church of God (1 Corinthians 10:32)? 

Because all things (authority) was given from God unto Christ. (Mat 28:18; Luke 1:32-33; John 3:35; 13:3, 17:2; 1Cor 15:27 NLT; Eph 1:22; Heb 2:8; 1Peter 3:22)